Avionics - Satellite Communication Quiz(MCQ)

1 .

What happens if a satellite is launched vertically and released at its design altitude?

A)

Fall back

B)

Continue to orbit the earth

C)

Stays where it was released

D)

Overshoots the altitude and moves at a constant speed

Correct Answer : Fall back

Explanation : If a satellite were launched vertically from the earth and then released, it would fall back to earth because of gravity. For the satellite to go into orbit around the earth, it must have some forward motion. For that reason, when the satellite is launched, it is given both vertical and forward motion.

2 .

Why does the orbit take the shape of an ellipse or circle?

A)

Consume less fuel

B)

Most efficient geometry

C)

Better coverage on earth

D)

Position can be easily determined

Correct Answer : Position can be easily determined

Explanation : A satellite rotates about the earth in either a circular or an elliptical path. Circles and ellipses are geometric figures that can be accurately described mathematically. Because the orbit is either circular or elliptical, it is possible to calculate the position of a satellite at any given time.

3 .

The direction of orbit in the same direction of earth rotation is called ______

A)

Perigee

B)

Apogee

C)

Posigrade

D)

Retrograde

Correct Answer : Posigrade

Explanation : The direction of satellite rotation may be either in the same direction as the earth’s rotation or against the direction of earth’s rotation. In the former case, the orbit is said to be posigrade, and in the latter case, retrograde. Most orbits are posigrade.

4 .

When is the speed of the satellite maximum in an elliptical orbit?

A)

Apogee

B)

Perigee

C)

Posigrade

D)

Retrograde

Correct Answer : Perigee

Explanation : In an elliptical orbit, the speed changes depending upon the height of the satellite above the earth. Naturally, the speed of the satellite is greater when it is close to the earth than when it is far away. The closest point is called the perigee.

5 .

The time period taken by the satellite to complete one orbit is called ________

A)

Time period

B)

Sidereal period

C)

Lapsed time

D)

Unit frequency

Correct Answer : Sidereal period

Explanation : The period is the time it takes for a satellite to complete one orbit. It is also called the sidereal period. A sidereal orbit uses some external fixed or apparently motionless object such as the sun or star for reference in determining a sidereal period.

6 .

What is the point on the surface of the earth that is directly below the satellite called?

A)

Subsatellite point

B)

Overhead point

C)

Satellite point

D)

Supersatellite point

Correct Answer : Subsatellite point

Explanation : The satellite location is specified by a point on the surface of the earth directly below the satellite. This point is known as the subsatellite point (SSP). The subsatellite point is then located by using conventional latitude and longitude designations.

7 .

What percentage of the earth can communication satellites see?

A)

20

B)

40

C)

50

D)

70

Correct Answer : 40

Explanation : Most communication satellites in use today are of the geosynchronous variety. Approximately 40 percent of the earth’s surface can be “seen” or accessed from such a satellite. Users inside that area can use the satellite for communication.

8 .

The period of time that elapses between the successive passes of the satellite over a given meridian of earth longitude is called as ________

A)

Time period

B)

Lapsed time

C)

Synodic period

D)

Sidereal period

Correct Answer : synodic period

Explanation : Another method of expressing the time for one orbit is the revolution or synodic period. One revolution (1 r) is the period of time that elapses between the successive passes of the satellite over a given meridian of earth longitude. Naturally, the synodic and sidereal periods differ from each other because of the earth’s rotation.

9 .

To use a satellite for communication relay or repeater purposes what type of orbit will be the best?

A)

Circular orbit

B)

Elliptical orbit

C)

Triangular orbit

D)

Geosynchronous orbit

Correct Answer : Geosynchronous orbit

Explanation : The best solution is to launch a synchronous or geostationary satellite. In a geosynchronous earth orbit. Since the satellite remains apparently fixed, no special earth station tracking antennas are required. The antenna is simply pointed at the satellite and remains in a fixed position. With this arrangement, continuous communication is possible.

10 .

The satellite that is used as a relay to extend communication distance is called as _____

A)

Relay satellites

B)

Repeater satellites

C)

Communication satellites

D)

Geosynchronous satellites

Correct Answer : Communication satellites

Explanation : Communication satellites are not originators of information to be transmitted. If a transmitting station cannot communicate directly with one or more receiving stations because of line-of-sight restrictions, a satellite can be used. The transmitting station sends the information to the satellite, which in turn re-transmits it to the receiving stations.

11 .

The transmitter-receiver combination in the satellite is known as a _______

A)

Transponder

B)

Relay

C)

Repeater

D)

Duplexer

Correct Answer : Transponder

Explanation : The transmitter-receiver combination in the satellite is known as a transponder. The basic functions of a transponder are amplification and frequency translation. The reason for frequency translation is that the transponder cannot transmit and receive on the same frequency.

12 .

What is the reason for carrying multiple transponders in a satellite?

A)

More gain

B)

Redundancy

C)

Better reception

D)

More number of operating channel

Correct Answer : More number of operating channel

Explanation : To be economically feasible, a satellite must be capable of handling several channels. As a result, most satellites contain multiple transponders, each operating at a different frequency. Each transponder represents an individual communication channel.

13 .

Why are VHF, UHF, and microwave signals used in satellite communication?

A)

More bandwidth

B)

Are not diffracted by the ionosphere

C)

Economically viable

D)

More spectrum space

Correct Answer : Are not diffracted by the ionosphere

Explanation : VHF, UHF, and microwave signals penetrate the ionosphere with little or no attenuation and are not refracted to earth. Lower frequencies undergo total internal refraction and get reflected back to earth.

14 .

What is the reason for shifting from c band to ku band in satellite communication?

A)

More bandwidth

B)

Overcrowding

C)

Lesser attenuation

D)

Less power requirements

Correct Answer : Overcrowding

Explanation : Most new communication satellites will operate in the Ku band. This upward shift in frequency is happening because the C band is overcrowded. Many communication satellites are in orbit now, most of them operating in the C band. However, there is some difficulty with interference because of the heavy usage. The only way this interference will be minimized is to shift all future satellite communication to higher frequencies.

15 .

Which technique uses spot beam antennas to divide the area covered by the satellite into smaller segments?

A)

Multiplexing

B)

Modulation

C)

Spatial isolation

D)

Frequency reuse

Correct Answer : Spatial isolation

Explanation : By using narrow beam or spot beam antennas, the area on the earth covered by the satellite can be divided up into smaller segments. Earth stations in each segment may actually use the same frequency, but because of the very narrow beam widths of the antennas, there is no interference between adjacent segments.

16 .

Which technique uses two different antennas to reduce traffic on the same frequency?

A)

Frequency reuse

B)

Modulation

C)

Multiplexing

D)

Spatial isolation

Correct Answer : Frequency reuse

Explanation : In the frequency reuse technique two systems use the same frequency, although operating on exactly the same frequencies, they are isolated from each other by the use of special antenna techniques. For example, a vertically polarized antenna will not respond to a horizontally polarized signal and vice versa. Or a left-hand circularly polarized (LHCP) antenna will not respond to a right-hand circularly polarized (RHCP) signal and vice versa.

17 .

Why are techniques like frequency reuse and spatial isolation carried out?

A)

More gain

B)

High speed

C)

Error detection

D)

Reduce traffic load

Correct Answer : Reduce traffic load

Explanation : At times there is more traffic than there are transponders to handle it. For that reason, numerous techniques have been developed to effectively increase the bandwidth and signal-carrying capacity of the satellite. Two of these techniques are known as frequency reuse and spatial isolation.

18 .

What is the maximum theoretical data rate if a transponder is used for binary transmission and has a bandwidth of 36MHz?

A)

12Mpbs

B)

32Mpbs

C)

36Mpbs

D)

72Mpbs

Correct Answer : 72Mpbs

Explanation : For binary transmission, the maximum theoretical data rate or channel capacity C for a given bandwidth B is C = 2B = 2(36) =72Mpbs.

19 .

Which of the following is not a satellite subsystem?

A)

Power system

B)

Ground station

C)

Telemetry tracking

D)

Communication subsystem

Correct Answer : Ground station

Explanation : The communication subsystem is the most important part of the satellite. It requires varies additional systems like the power system, propulsion system, telemetry system for its proper functioning. The ground system however is not one of the satellite subsystem and is independent of the satellite. It is just a transponder to monitor and command the satellite.

20 .

Which of the following is not a part of the propulsion subsystem of a satellite?

A)

AKM

B)

Jet thruster

C)

Gyroscope

D)

Fuel control system

Correct Answer : Gyroscope

Explanation : The propulsion subsystem consists of the AKM(Apogee kick motor), jet thruster and the fuel control system. Gyroscopes and other attitude systems fall under the attitude control subsystem.

21 .

Which of the following are common baseband signals transmitted from the earth ground station?

A)

Computer data

B)

Computer data, navigational data, voice

C)

Voice, video, computer data

D)

Navigational data, computer data, video

Correct Answer : Voice, video, computer data

Explanation : An earth station takes the signals to be transmitted, known as baseband signals, and modulates a microwave carrier. The three most common baseband signals are voice, video, and computer data.

22 .

Which of the following components receives, translates the signal frequency and re-transmits the signal in a satellite?

A)

Transponder

B)

Relay

C)

Repeater

D)

Transducer

Correct Answer : Transponder

Explanation : The uplink signals from earth are amplified, translated in frequency, and re-transmitted on the downlink to one or more earth stations. The component that performs this function is known as a transponder.

23 .

Why is it not possible to provide transmit function by wideband amplifier and mixer circuits?

A)

Heavy attenuation

B)

Economically not profitable

C)

Weight of the system increases five fold

D)

High power output over wideband is not possible

Correct Answer : High power output over wideband is not possible

Explanation : it is generally not possible to generate very high output power over such wide bandwidth. The fact is that no components and circuits can do this well. The high-power amplifiers in most transponders are traveling-wave tubes that inherently have limited bandwidth. They operate well over a small range but cannot deal with the entire 500-MHz bandwidth allocated to a satellite.

24 .

Which of the following transponders convert the uplink signal to downlink signal using two mixers

A)

Dual mixer transponder

B)

Dual conversion transponders

C)

Regenerative transponders

D)

Single conversion transponders

Correct Answer : Dual conversion transponders

Explanation : A dual-conversion transponder makes the frequency translation in two steps with two mixers. No demodulation occurs.

25 .

Why is there a huge spectrum space between the transmitted and received signal in satellite communication?

A)

Less attenuation

B)

Reduce interference

C)

Maximum efficiency

D)

To reduce space occupied by filters

Correct Answer : Reduce interference

Explanation : Because of the close proximity of the transmitter and the receiver in the satellite, the high transmitter output power for the downlink is picked up by that satellite receiver. Naturally, the uplink signal is totally obliterated. Furthermore, the transmitter output fed back into the receiver input causes oscillation. To avoid this problem, the receiver and transmitter in the satellite transponder are designed to operate at separate frequencies. In this way, they will not interfere with each other.

26 .

What is the use of the band pass filter in the receiver section?

A)

Reduces noise

B)

Increases antenna gain

C)

Protects the receiver

D)

To reduce it to an intermediate frequency

Correct Answer : Protects the receiver

Explanation : The diplexer feeds a bandpass filter (BPF) in the receiver section that ensures that only the received frequencies pass through to the sensitive receiving circuits. This bandpass filter blocks the high-power transmit a signal that can occur simultaneously with reception. This prevents overload and damage to the receiver.

27 .

In Rf tuning, what is the first local oscillator?

A)

Frequency synthesizer

B)

Quartz oscillator

C)

Electric oscillators

D)

Magnetic oscillator

Correct Answer : Frequency synthesizer

Explanation : In RF tuning, the first local oscillator is made adjustable. Generally, a frequency synthesizer is used in this application. The frequency synthesizer generates a highly stable signal at selected frequency increments.

28 .

Which of the following amplifiers is used in the transmitter substation?

A)

RF amplifiers

B)

Buffer amplifiers

C)

Klystron amplifier

D)

Operational amplifiers

Correct Answer : Klystron amplifier

Explanation : The signals to be sent to the satellite might be TV programs, multiple telephone calls, or digital data from a computer. These signals are used to modulate the carrier, which is then amplified by a large traveling-wave tube or klystron amplifier.

29 .

Which part of the transmitter subsystem modulates the baseband signal?

A)

Mixer

B)

Antenna

C)

Power amplifiers

D)

Up converter

Correct Answer : Up converter

Explanation : The transmit subsystem consists of two basic parts, the up converters and the power amplifiers. The up converters translate the baseband signals modulated on to carriers up to the final uplink microwave frequencies.

30 .

In RF tuning, _________ provides the final up conversion to the microwave frequency?

A)

Quartz oscillator

B)

RF frequency synthesizer

C)

Magnetic oscillator

D)

Fixed-frequency local oscillator

Correct Answer : RF frequency synthesizer

Explanation : In RF tuning, a mixer fed by a fixed-frequency local oscillator performs an initial up conversion to 700 MHz. Then a sophisticated RF frequency synthesizer applied to a second mixer provides up conversion to the final microwave frequency.

31 .

When individual up converters are used to modulate a channel, what is used to combine them into final signal?

A)

Mixer

B)

Microwave combiner

C)

Amplifier

D)

Multiplexer

Correct Answer : Microwave combiner

Explanation : Individual up converters are used on each modulated channel. At the output of the up converters, all the signals are combined in a microwave combiner, which produces a single output signal that is fed to the final amplifiers.

32 .

What is the primary use of communication satellites?

A)

GPS

B)

Research

C)

Surveillance

D)

Telephone service

Correct Answer : Telephone service

Explanation : The primary use of communication satellites is in long-distance telephone service. Satellites greatly simplify long-distance calls not only within countries but also worldwide.

33 .

Which of the following is not a reason for redistributing TV signals through satellites rather than skywaves or spacewaves?

A)

Power requirements

B)

Economically feasible

C)

High frequency signal

D)

Long distance communication

Correct Answer : Power requirements

Explanation : TV signals are being transmitted through satellites for redistribution. Because of the very high-frequency signals involved in TV transmission, other long-distance transmission methods are not technically or economically feasible.

34 .

What type of satellite TV service uses compressed data transmission to beam signals directly to every home?

A)

Fixed satellite service

B)

Mobile satellite service

C)

Direct broadcast satellite

D)

Broadcasting satellite service

Correct Answer : Direct broadcast satellite

Explanation : The direct broadcast satellite (DBS) system is an all-digital system. Data compression techniques are used to reduce the data rate in order to produce high-quality picture and sound. They uses special broad coverage satellites with high power to transmit cable-TV-like services direct to homes equipped with the special DBS receivers.

35 .

Which frequency band does the direct broadcast satellite system use?

A)

C band

B)

X band

C)

Ku band

D)

MF band

Correct Answer : Ku band

Explanation : The DBS satellite uses the Ku band with a frequency range of 11 to 14 GHz. Uplink signals are usually in the 14- to 14.5-GHz range, and the downlink usually covers the range of 10.95 to 12.75 GHz.

36 .

What technique does DSP use to double the number of channels by using helical antennas?

A)

Modulation

B)

Frequency reuse

C)

Multiplexing

D)

Spatial isolation

Correct Answer : Frequency reuse

Explanation : The digital signal is transmitted from the satellite to the receivers using circular polarization. The DBS satellites have right-hand and left-hand circularly polarized (RHCP and LHCP) helical antennas. By transmitting both polarities of signal, frequency reuse can be incorporated to double the channel capacity.

37 .

What is the number of satellites present in the Iridium system?

A)

72

B)

66

C)

51

D)

32

Correct Answer : 66

Explanation : The satellite systems use low-earth-orbit satellites to perform the relay services to the main telephone system or to make a connection directly between any two cellular telephones using the system. One of the oldest and most widely used is the Iridium system. It uses a constellation of 66 satellites in six polar orbits with 11 satellites per orbit 420 mi above the earth.

38 .

What provides the sufficient drive to the final power amplifier?

A)

Up converter

B)

Power driver circuit

C)

Operational amplifier

D)

Intermediate-power amplifier

Correct Answer : Intermediate-power amplifier

Explanation : The power amplifier usually begins with an initial stage called the intermediate-power amplifier (IPA). This provides sufficient drive to the final high-power amplifier (HPA).

39 .

Which frequency band is used for connecting the satellite system with the public switched telephone network?

A)

Ka band

B)

L band

C)

C band

D)

Ku band

Correct Answer : Ka band

Explanation : The satellites communicate with ground stations called gateways that connect the system to the public switched telephone network. The satellites also communicate among themselves. Both gateway and intersatellite communication takes place over Ka band frequencies.